Segmented polyurethane elastomers based on polyether and polyester diols

ABSTRACT

Polyurethane elastomers are prepared by reacting a prepolymer (A) of a polyether diol and a diisocyanate with a mixture (B) of a polyester diol and a lower molecular weight glycol at a temperature of from about 60*C. to about 180*C. The reaction product of (A) and (B) is resistant to separation and the polyurethane elastomers combine all of the advantageous properties of both polyether polyurethanes and polyester polyurethanes and are useful as foils and coatings and can be molded into a variety of elastomeric products.

United States Patent Meisert et al.

[54] SEGMENTED POLYURETHANE ELASTOMERS BASED ON POLYETHER AND POLYESTERDIOLS Inventors: Ernst Meisert, Leverkusen; Albert Awater,Cologne-Muelheim; Cornelius Muhlhausen, Leverkusen; Uwe JensDiibereiner, Opladen, all of Germany Farbenlabriken BayerAktiengesellschaft, Leverkusen, Germany Filed: July 30, 1970 Appl. No.:59,666

Assignee:

Foreign Application Priority Data May 7, 1969 Germany ..P 19 40181.1

US. Cl. ..260/75 NP, 8/115.6, 260/77.5 AM, 260/775 D rm. Cl. ....cs22/10, C08g 22/14, C08g 22/16 Field of Search .....260/75 TN, 77.5 AM,77.5 D

References Cited UNITED STATES PATENTS /1962 Schmidt et al ..260/753,684,770 1 Aug. 15, 1972 3,541,183 11/1970 Kallert et a1 ..260/8582,729,618 1] 1956 Mueller el al. ..260/ 2,888,432 5/1959 Fauser..260/45.4 2,917,489 12/1959 Gladding et al. ..260/77.5 2,929,800 3/1960Hill ..260/77.5 2,948,691 8/1960 Windemuth et a1. ..260/ 2.5 2,953,5399/1960 Keplinger et a1. 2 ..260/3 1.6 3,192,185 6/ 1965 Achterhof et a1.260/ 75 3,248,373 4/1966 Barringer ..260/ 77.5 3,544,524 12/ 1970Mueller et a1. ..260/77.5

Primary Examiner-Donald E. Czaja Assistant Examiner-H. S. CockeramAttorney-Robert A. Gerlach [57] ABSTRACT 6 Claims, No Drawings SEGMENTEDPOLYURETHANE ELASTOMERS BASED ON POLYETHER AND POLYESTER DIOLS Thisinvention relates to elastomeric polyurethanes and more particularly topolyurethane elastomers based on polyether prepolymers in admixture withpolyester diols.

The production of polyurethane elastomers by reacting a prepolymer ofpolyetheror polyester-diols and excess diisocyanate with low molecularweight glycols is well known in the art. Polyurethanes based onpolyesters are, however, very liable to hydrolytic decomposition, areeasily decomposed by schizomycetes and have a marked tendency tocracking when stretched, especially if, at the same time, they areexposed to moisture. In addition many polyesterpolyurethane elastomershave a marked tendency to crystallization and hardening and have only avery low flexibility at low temperature.

Polyurethane elastomers based on polyether diols which have a goodresistance to hydrolysis are, how ever, more susceptible to the actionof hot air and undergo more swelling in organic solvents and in waterthan polyester polyurethanes and also have less mechanical strength.

Obvious attempts to produce polyurethanes from mixtures of polyethersand polyesters, however, cannot be carried out easily since the diolcomponents usually separate out and it is difficult to find areproducible method of preparation owing to the varying reactivity ofdiols.

Subsequent attempts to mix thermoplastically deformable polyurethanesbased on polyethers with polyurethanes based on polyesters also givevery unsatisfactory results because the polyester urethanes separatefrom the polyether urethanes in molded products which have been producedin this way, and products made from such mixtures therefore often havesevere structural anisotropy.

It is also obvious to assume that mixtures of polyether and polyesterurethanes would manifest the undesirable properties both of the purepolyether polyurethanes and of the polyester polyurethanes. In the caseof some properties, such as, for example, the resistance to hydrolysis,one would even expect the mixing itself to have an undesirable effectsince the hydrophilic polyether constituents could reinforce thetransfer of the attacking agent to the sensitive polyester segments.

It is therefore an object of this invention to provide polyurethaneelastomers based on polyethers and polyesters devoid of the foregoingdisadvantages. It is another object of this invention to providepolyurethane elastomers combining the advantageous properties of bothpolyether polyurethanes and polyester urethanes. A further object ofthis invention is to provide polyurethane elastomers having good coldflexibility and high resistance to abrasion and tear propagation. Stillanother object of this invention is to provide polyurethane elastomershaving a high resistance to fats, oils and solvents. Yet another objectof this invention is to provide polyurethane elastomers wherein thetendency toward cracking is conspicuously low.

The foregoing objects and others are accomplished in accordance withthis invention, generally speaking by providing a polyurethane elastomerwhich comprises the steps of (A) preparing a polyether prepolymer byreacting about 1 mol of polyether diol having a molecular weight of fromabout 800 to about 3,500 or a polyether diol mixture with from about 3to about 20 mols of a diisocyanate at a temperature of from about 60C.to about C; (B) preparing a mixture of from about 0.5 to about 2.5 molsof a polyester diol having a molecular weight of from about 800to about3,500 and from about 1.5 to about 14.5 mols of a glycol having amolecular weight of less than about 300; and (C) reacting togethercomponents A. and B., at a temperature of from about 60C. to about180C., such that the NCO to OH ratio is from about 0.95 to about 1.1.

The process of the invention is surprising in that polyurethaneelastomers having very advantageous physical properties can be obtainedin a reproducible manner. The process of the invention also has severaladvantages over heretofore known processes for producing polyurethaneelastomers based on mixtures of polyethers and polyesters, such as, forexample, eliminating the processing difficulties caused by the tendencyof prior art mixtures of polyesters and polyethers to separate intotheir components; and facilitating dosing and mixing of the components,resulting in a more easily controllable reaction as to component A.,since the comparatively inert OH groups preferably present in thepolyether diol are reacted with a relatively large excess of isocyanate,and in component B., the concentrations of the highly reac' tive primaryOH groups of the glycol are reduced by dilution with the polyesters.

The present invention thus relates to a process for the production ofpolyurethane elastomers from diisocyanates, polyether diols having amolecular weight of from about 800 to about 3,500andl polyester diolshaving a molecular weight of from about 800 to about 3,500 and glycolshaving a molecular weight below about 300, wherein, in a first reactionstage a prepolymer (A) is prepared from about 1 mol of polyether dioland from about 3 to about 20 mols of diisocyanate at temperatures offrom about 60 to about 180C. and this prepolymer is then reacted in asecond reaction stage with (B) a mixture of from about 0.5 to about 2.5mols of polyester diol and from about 1.5 to about 14.5 mols of glycolat a temperature of from about 60C. to about 180C., an overall NCO/OHratio calculated over both reaction stages of 0.95 to 1.1 being used.

It is not essential that all of the diisocyanate be reacted at once withthe polyether diol in the first reaction stage but at least about 2.2mols of diisocyanate should be used per mol of polyether diol. Thequantity of diisocyanate required for the second reaction stage, i.e.sufficient to give an NCO/OH ratio of from about 0.95 to about 1.1, maythen be added to the prepolymer before reaction.

The polyurethanes synthesized by the process according to the inventionmainly have structural segments represented by formulas l and (2):

A represents the radical which is obtained by removal of the hydroxylgroups from a dihydroxy polyether,

E represents the radical which is obtained by removal of the hydroxylgroups from a dihydroxy polyester,

R represents the radical which is obtained by removal of the hydroxylgroups from a glycol,

Q represents the radical which is obtained by removal of the isocyanategroups from a diisocyanate and n is a positive integer. Thesepolyurethanes are the so-called block polymers, the hard segment ofwhich contains the urethane blocks represented by formula (3):

(3) OR-O[-CONHQNHCOOR O-],, CO... and soft segment or polyester andpolyether groups. Since polyethers and polyesters are generally notsoluble in each other or are only soluble to a slight extent, thecomponents of this soft segment are present entirely or partly in theseparated state. This renders the formation of large crystalline regionsvery difficult, with the result that these polyurethane elastomers areusually distinguished by particularly high transparency and have goodflexibility even at low temperatures.

Any polyether polyols may be used for the process according to theinvention. Adducts of ethylene oxide or propylene oxide with initiatormolecules such as, for example, water, glycol, l ,2-propanediol, 1,3-propanediol, glycerol, trimethylol propane, and the like areparticularly suitable. Butylene glycol polyethers and mixed polyetherswhich in addition to the above mentioned components also have otherglycol radicals incorporated in them, such as, for example, phenyl,ethylene glycol radicals and the like are also suitable.

Dihydroxy polyesters are preferably used. Particularly suitabledihydroxy polyesters are polyesters which are obtained from dicarboxylicacids such as, for example, succinic acid, adipic acid, cyclohexanedicarboxylic acid, terephthalic acid, and the like and diols such as,

for example, ethylene glycol, 1,2-propylene glycol, 1,3-

propylene glycol, 1,4-butylene glycol, 1,5-pentanediol, 1,6-hexanediol,hydroquinone-bis-hydroxyethyl ether, diethylene glycol, triethyleneglycol and the like are given as examples of low molecular weightglycols (molecular weight less than about 300). These alkylene glycols,as the polyesters, should have exclusively primary OH groups.

The preparation of prepolymer (A) from the polyether glycol and thediisocyanate may be carried out continuously or intermittently attemperature of from about 60C. to about 180C. In the case ofintermittent preparation, the diol is advantageously introducedgradually into the liquid or molten diisocyanate. If the polyethercontains secondary OH groups, reaction times of from about 45 to aboutminutes are required at a preferred reaction temperature of about 100C.If the highly reactive aromatic diisocyanates are used, it is notnecessary to catalyze the reaction. When using the less reactivealiphatic diisocyanates, it is advisable to carry out the reaction at atemperature of about C. or to include known catalysts such as, forexample tin dibutyl dilaurate, tin dioctoate, alkali metal salts ofcarboxylic acid, and the like.

The reaction of polyether prepolymer (A) with the polyester glycolmixture (B) is advantageously carried out at temperatures of from about60C. to about C. Since the reaction proceeds rapidly and is vigorouslyexothermic, it may be carried out continuously or intermittently byrapid and intensive mixing of the components and then immediatelypouring them into molds heated to from about 80C. to about 120C., or onto warm plates or the like. The reaction mixture solidifies within a fewminutes and forms high grade elastomers. Finished products, foils andplates can be produced directly in this way. The elastomers obtainedmay, if desired, be first broken up into small pieces and then shapedtherrnoplastically, such as, for example by extrusion, injection moldingor calendering. They are soluble in strongly polar solvents such asdimethyl formamide or mixtures of dimethyl forrnamide and cyclohexanone.Such solutions can be worked up in known manner into foils, coatings andthe like.

When using NCO/OH ratios of from about 0.95 to about 1.0, types ofurethane rubbers are obtained which can be worked up by known methodsused in the rubber industry.

The products of the process are therefore useful for the production oftubes, cable sheathings, buffers, protective flaps, friction bearings,damping transmission elements, shoesoles, textile coatings and the like.

The invention is further illustrated but it is not intended that it belimited by the following Examples in which all parts and percentages areby weight unless otherwise specified.

EXAMPLE la About 100 parts of a mixture (OH number 92, average molecularweight L220) of a linear polypropylene glycol ether of molecular weight2,000

and a linear polypropylene glycol ether of molecular weight 890 areheated to about 100C. and introduced into about 119.5 parts of4,4-diisocyanato-diphenylmethane heated to about 60C. and the reactantsare mixed. The reaction temperature rises to about 120C. 5

reaction mixture solidifies within a short time and is removed from themold after about 5 to minutes.

A part of the cooled molded product is granulated with an impellerbreaker and worked up in injection molding and extrusion machines. Thefinished articles have excellent transparency and good mechanical.

strength. lb Test for Comparison with 1a t A polyether, a polyester anda butylene glycol of the same type and in the same proportions asv inExample 1a are mixed, heated to about 120C. and stirred together forabout seconds with 4,4'-diisocyanatodiphenylmethane which is heated toabout 120C. The mixture is poured'into molds which are at a temperatureof about 120C. The products solidify to a waxy consistency and havelittle mechanical strength. 10 Test for Comparison with 1a l About 100parts of the polyester of Example 1a is heated to about 100C. andintroduced into about 119.5 parts of 4,4-diisocyanatodiphenylmethanewhich is heated to about 60C., and the mixture is stirred. Thetemperature rapidly rises to about 132C. The prepolymer is heated toabout 135C. and a mixture of about 100 of the polypropylene glycol ethermixture from Example 1a and about 30 parts of butane-l,4-diol which is.at a temperature of about 120C. are stirred together for about 30seconds and the mixture is poured into molds which are at a temperatureof about 110 to 120C. Subsequent working up is carried out as in Examplela. The products are semi-opaque and have little mechanical strength.

The results of the physical testing of the products prepared accordingto Examples la to 1c are summarized in Table 1.

with a mixture which is heated to about 100C. of about 45 parts ofbutane-1,4-diol and about 100 parts of a polyester of adipic acid andethanediol (OH number 112, molecular weight 1,000), and poured on toplates which are at a temperature of about 120C. The reaction productmay be lifted off after about 5 minutes.

When cold, the-product is granulated and worked up into test samples ininjection molding machines.

10 2b Test for Comparison with 2a The procedure is the same as inExample2a but about 100 parts of the polyester are replaced by the equivalentquantity of a propylene glycol ether (OH number 110). Only a waxy massis obtained, the 5 mechanical properties of which could not be tested.

2c Test for Comparison with 24 About 100 parts of polypropylene glycolether (molecular weight 2,000, 01-1 number 56) and about IOO parts ofpolypropylene glycol ether(molecular weight 1,020, OH number 110) arereacted with about 173 parts of 4,4-diisocyanato-diphenylmethane atabout 120C. and the reaction mixture is heated at about 120C. for aboutminutes and then im- 25 mediately mixed with about 45 parts ofbutane-1,4-

dio1.-The product is poured on to plates which are at a temperature ofabout 120C. After about 10 minutes, it is lifted off, cooled, granulatedand molded.

2d Test for Comparison with 2a The procedure is the same as in Example2a but instead of polypropylene glycol polyether, a polyester of adipicacid and ethylene glycol (molecular weight 2,000, OH number 56, acidnumber 0.9) is used. The

35 values obtained are shown in the table below:

Test Accord- Example ing to DIN Dimension 2a 2b 2c 2d Shore hardness 53505 A 97 96 Tensile strength 53 504 kg wt/cm 492 268 410 Elongation atbreak 53 504 510 141 4'80 Loss by abrasion 53 516 mm 39 104 Additionaltests:

50 Test samples from Examples 2a to 2d were stored in TABLE 1Examination Example according Properties tested to DIN Dimension la 11)10 Appearance. 'llilllSllill'OlllL. 'Wnxy,opaquo; Opaque. Shore hardnessA 53,505 88.. 86 84. Tensile strength 53, 504 Kg.Wl2./C111. 392. 192.Tear propagation resistance 53, 515 Kg. Wt./(3l1l... 69. .r 20-40. Lossby abrasion 53, 516 "1111- 38 94.

EXAMPLE 2&

water at about 100C. and the time for the tensile strength to drop toabout 200 kg wt/cm was determined:

t (days)= 3-4 Test samples from Examples 201 to 2d were buried under apretension of about 50 percent in moist garden soil. After about 3months, the attack by schizomycetes and formation of cracking weredetermined. The samples from experiments 2a and 2c show no damage butthe samples from experiments 2d are attacked by schizomycetes and showcracks transverse to the direction of stretching. Sample 2b is brokenright through but shows no attack by mold.

EXAMPLE 3 A mixture of about 33.8 parts of a linear polypropylene glycolether of molecular weight 2000 and about 14.7 parts of a trifunctionalpolypropylene glycol ether of molecular weight 2,000 are stirred forabout one hour at about 140C. with'about 24 parts ofhexamethylene-l,6-diisocyanate. The prepolymer produced is treated withabout 1 part of 2,, 6-2, 6- tetraisopropyl-diphenylcarbodiimide andstirred together for about 120 secondswith a solution which is heated toabout 120C. of about 0.01 part of sodium acetate in about 8 parts ofbutane -1,4-diol and about 46.5 parts of a hexanediol polycarbonate(molecular weight 2,000) which have terminal hydroxyl groups. Themixture is then poured out on plates which are at a temperature of about110C. The product may be stripped froma plate after about 8 minutes. Thefollowing mechanical properties are determined on the elastictransparent synthetic material:

Tensile strength (kg wt/cm; DIN 53 504): 248

Elongation at break (36; DlN 53 504): 560 Tear propagation resistance(kg wt/cm; DIN 53 515): 58

Shore hardness A (DIN 53 505) 81 EXAMPLEA The same procedure wasemployed as in Example 3 but about 18.2 parts of the linearpolypropylene glycol ether (molecular weight 2,000), about 19.2 parts ofthe trifunctional polypropylene glycol ether (molecular weight 2,000)and about 62.6 parts by weight of the hexanediol polycarbonate are used.The elastic, transparent material is granulated and extruded into bandswhich are about 2 mm in thickness and about 32 mm in width. Theproperties of these bands are tested as follows:

Tensile strength (kg wt/cm; DIN 53 504): 220

Elongation at break DIN 53 504): 400 Tear propagation resistance (kgwt/cm; DIN 53 515): 50

Shore hardness A (DIN 53 505): 85

The test samples from Examples 3 and 4 were stored in water at about100C. for about 7 days. The mechanical properties were unchanged at theend of this time.

EXAMPLE A prepolymer of about 43 parts of a linear polypropylene glycolether of molecular weight 2,000 and about 35.6 parts of4,4Fdiisocyanato-diphenylmethane is prepared at about 120C, stirred atabout 20 mm Hg for' about 30 minutes and treated with about 1 part of2,2, 6,6-tetraisopropyl-diphenylcarbodiimide. The propolymer at atemperature of about 125C. is then stirred for about 45 seconds with amixture which is heated to about 125C. of about 8 parts ofbutane-1,4-diol and about 57 parts of a polyester of 8 adipic acid,butanediol and ethane diol (molecular weight 2,000, OH number 56).Plates 1, 2, 4 and 6 mm in thickness are cast in the course of about 1minute (molding temperature 120C). They may stripped after about 10minutes. The test samples were stored at about 90C. for about 15 hoursand then tested.

Tensile strength (kg wt/cm; DIN 53 $04): 281 Elongation at break DIN 53504): 480 Tear propa ation resistance (kg wt/cm; IN 53 515): 48 Shorehardness (DIN 53 504): 76

In the soil corrosion test, i.e. storage in moist garden EXAMPLE 6Example 5 is repeated, but instead of about 35.6 parts of4,4'-diisocyanato-diphenylmethane (NCO/OH 1.03), only about 34.8 parts(NCO/OH 0.97) are used. The molded products are granulated, and about a20 percent solution in dimethyl formamide is prepared by dissolving thegranules at about 90C. After painting the solution on glass plates anddrying, very thin flexible and very stretchable films are obtained whichare insoluble in trichloroethylene, petroleum hydrocarbons and oil.

Although the invention has been illustrated in considerable detail bythe foregoing it is to be understood that such detail is solely forthepurpose of illustration and that one skilled in the art may make manyvariations therein without departing from the spirit and scope of theinvention.

What is claimed is:

l. A polyurethane elastomer prepared by a process which comprisespreparing, in a first reaction stage a propolymer (A) of 1 mol of apolyether diol having a molecular weight of from about 800 to about3,500 and from about 3 to about 20 mols of a diisocyanate at atemperature of from about C. to about 180C. and reacting (A) in a secondreaction stage with a mixture (B) of from about 0.5 to 2.5 mols of apolyester diol,

having a molecular weight of from about 800 to about 3,500, and a glycolhaving a molecular weight of less than about 300, at a temperature offrom about 60C. to about 180C., such that an NCO to OH ratio of fromabout 0.95 to about 1. 1 ratio calculated over both reaction stages isused.

2. The elastomer of claim 1 wherein the diisocyanate is 4,4-diisocyanatodiphenylmethane.

3. The elastomer of claim 1 wherein the polyether diol is apolypropylene glycol ether or a mixture of polypropylene glycol ethers.

4. The elastomer of claim 1 wherein the mixture (B) is a mixture of apolyester of adipic acid and butane-

2. The elastomer of claim 1 wherein the diisocyanate is4,4''-diisocyanato diphenylmethane.
 3. The elastomer of claim 1 whereinthe polyether diol is a polypropylene glycol ether or a mixture ofpolypropylene glycol ethers.
 4. The elastomer of claim 1 wherein themixture (B) is a mixture of a polyester of adipic acid andbutane-1,4-diol.
 5. The elastomer of claim 1 wherein the polyester diolis a hexanediol polycarbonate.
 6. The elastomer of claim 1 wherein theglycol is butane-1,4-diol.